The fatty acid composition of blood and tissue lipids of patients with cystic fibrosis has been shown to be abnormal. The predominant alterations include a decreased linoleic acid and increased palmitoleic and oleic acids. These alterations are primarily due to the malabsorption and maldigestion associated with pancreatic insufficiency in the cystic fibrosis patient and are not corrected by exogenous pancreatic enzyme supplementation. The major unsaturated fatty acid within phospholipids, and thus within membrane lipids is linoleic acid. Decreased linoleic acid content as observed in most cystic fibrosis patients is thus associated with decreased unsaturation in tissue phospholipids and membranes. This characteristic may be related to alterations in membrane function as well as altering prostaglandin synthesis. Current work is aimed at delineating the role of altered fatty acid composition of blood and membrane lipids as a cause of decreased responsiveness of leukocytes to stimulation by isoproterenol, alterations in the recognition or interaction of the beta-receptors in CF tissues, and alteration in the availability of arachidonic acid for the biosynthesis of prostaglandin.